NO oxidation properties of Pt(111) revealed by ab initio kinetic simulations -: art. no. 115406

As a well-known oxidation catalyst, platinum is currently being used to convert NO to NO2 for absorption in so-called NOx traps under excess oxygen conditions, where direct conversion of NO to nitrogen gas is prohibitive. By performing kinetic Monte Carlo simulations with parameters derived from density-functional theory, we show that this oxidation process is not an inherent property of the platinum catalyst itself. In fact, the intrinsic NO+O -> NO2 reaction is found to be inhibited (endothermic) rather than promoted on Pt(111), due to strong oxygen-platinum bonds. Only at sufficient oxygen chemical potential does platinum become an efficient oxidation catalyst, as its oxygen bonds are weakened with increasing coverage, and the NO2 formation reaction becomes exothermic. At that point, Pt catalyzes the reaction by lowering the activation barrier for the kinetic reaction. Congruent with flow-reactor experiments, we note a strong temperature dependence for the turnover frequency, which should encourage further ultra-high vacuum studies.